21.16 Updating and accessing 2D histogram elements

You can access the bins of a two-dimensional histogram either by
specifying a pair of (x,y) coordinates or by using the bin
indices (i,j) directly. The functions for accessing the histogram
through (x,y) coordinates use binary searches in the x and y
directions to identify the bin which covers the appropriate range.

This function updates the histogram h by adding one (1.0) to the
bin whose x and y ranges contain the coordinates (x,y).

If the point (x,y) lies inside the valid ranges of the
histogram then the function returns zero to indicate success. If
(x,y) lies outside the limits of the histogram then the
function returns GSL_EDOM, and none of the bins are modified. The
error handler is not called, since it is often necessary to compute
histograms for a small range of a larger dataset, ignoring any
coordinates outside the range of interest.

This function returns the contents of the (i,j)-th bin of the
histogram h. If (i,j) lies outside the valid range of
indices for the histogram then the error handler is called with an error
code of GSL_EDOM and the function returns 0.

These functions find the upper and lower range limits of the i-th
and j-th bins in the x and y directions of the histogram h.
The range limits are stored in xlower and xupper or
ylower and yupper. The lower limits are inclusive
(i.e. events with these coordinates are included in the bin) and the
upper limits are exclusive (i.e. events with the value of the upper
limit are not included and fall in the neighboring higher bin, if it
exists). The functions return 0 to indicate success. If i or
j lies outside the valid range of indices for the histogram then
the error handler is called with an error code of GSL_EDOM.

Function: double gsl_histogram2d_xmax(const gsl_histogram2d * h)

Function: double gsl_histogram2d_xmin(const gsl_histogram2d * h)

Function: size_t gsl_histogram2d_nx(const gsl_histogram2d * h)

Function: double gsl_histogram2d_ymax(const gsl_histogram2d * h)

Function: double gsl_histogram2d_ymin(const gsl_histogram2d * h)

Function: size_t gsl_histogram2d_ny(const gsl_histogram2d * h)

These functions return the maximum upper and minimum lower range limits
and the number of bins for the x and y directions of the histogram
h. They provide a way of determining these values without
accessing the gsl_histogram2d struct directly.